The problems created by discarded or waste tires are well known. However, the problem continues to grow as more and more waste tires accumulate, thereby placing increasing pressure on landfills and waste dumps. It has been estimated that on the order of 250 million tires are discarded to become scrap or waste each year and that, over the years, billions of waste tires have accumulated.
A number of approaches have been taken in attempting to develop an efficient, cost effective and environmental acceptable way in which to dispose of tire scrap or waste. Many of these developments are the subject of patents, including the following U.S. Pat. Nos.: 3,843,457 to Grannen et al; 4,118,282 to Wallace; 4,647,443 (Apffel); 4,826,573 to Schippers; 4,839,151 to Apffel; 5,084,140, 5,084,141, 5,330,623, 5,387,321, and 5,364,821, all to Holland, 5,167,772 to Parker, Sr.; 5,316,224 to Dobozy; and 5,366,595 to Padgett et al. These patents themselves reference a number of other patents and other prior art of interest.
As indicated above and is explained in more detail below, the present invention employs microwave energy in the distillation of tires. Some of the patents listed above also use microwave energy for pyrolysis for various purposes. For example, the Apffel patents disclose a process for recovering char, oil and fuel gas for vehicle tires wherein the tires are first pyrolyzed using radiant heat to partially devolatize a major portion of the hydrocarbons in the tires and produce a char that can be separated from the steel, fiberglass and the like. The char can then be pyrolyzed with microwaves to devolatize the remaining hydrocarbons from the char as gas. A number of the Holland patents which relate to waste tire “compound” or scraps (e.g., U.S. Pat. Nos. 5,084,140, 5,084,141, and 5,330,623) disclose a process for the destructive distillation of such waste tire materials in bulk or chopped form wherein the materials are pre-heated without pyrolysis using a hot gas stream and then conveyed by a conveyor to a microwave discharge zone for pyrolysis. The Padgett et al. patent discloses an apparatus for pyrolyzing waste tires wherein the tires are placed in a rotating cylinder or drum and a microwave heating device is used to heat the material within the drum so as to break down the material into solid and fluid products.
The prior art processes and devices described above suffer a number of disadvantages. For example, relatively expensive high temperature equipment is often required, efficiencies are relatively low and costs relatively high, and, in some instances, environmental concerns are presented. Briefly considering the patents discussed specifically above, the use of radiant heat pyrolysis prior to microwave pyrolysis as in the Apffel patents has a number of drawbacks, including those discussed in some of the Holland patents (see, e.g., U.S. Pat. No. 5,084,141). Further, the processes disclosed in the Holland patents have disadvantages regarding cost and efficiency. For example, referring again to U.S. Pat. No. 5,084,141 to Holland, the use of straight line or linear conveyor belt and radiation chamber arrangement makes it difficult to provide microwave coverage of a whole tire and, in this regard, while the patent refers to the pyrolysis of tire material in bulk as well as in shredded form, the inline microwave energy pattern provided, as well as other aspects of the system, would appear to be specifically adapted to use with shredded tires or scrap tire chunks. The rotating metal drum arrangement of the Padgett et al. patent creates a number of problems, particularly with respect to establishing a stable standing wave ratio.